Annalisa Cardellini1 Matteo Fasano1 Matteo Alberghini1 Eliodoro Chiavazzo1 Pietro Asinari1

1, Politecnico di Torino, Torino, , Italy

In this talk, a ‘’good’’, a ‘’bad’’ and an ‘’ugly’’ stories will be telling around the behaviour of water at nanoscale solid-liquid interfaces. The understanding of water transport in nanoconfined configurations has revealed a prominent significance to predict the performance of biomedical phenomena and to guide the rational design of other engineering devices.

First, molecular dynamics simulations are used to compute the self-diffusion coefficient of water within nanopores, around nanoparticles, carbon nanotubes and proteins. For almost 60 different cases, the diffusion coefficient is found to scale linearly with a dimensionless parameter which represents the confinement degree of the water molecules [1]. Such relationship, coupled with the ‘’good’’ understanding of water transport behaviour, has shown to accurately predict the response of contrast agents for magnetic resonance imaging [1]. Later on, this relationship has been experimentally and independently validated by the Oak Ridge National Laboratory, beyond biomedical applications [2].

Second, experiments and atomistic simulations are used to elucidate the non-trivial interplay between nanopore hydrophilicity and the overall water transport through zeolite crystals. A poor correspondence between the experiments and simulations has suggested the presence of a ‘’bad’’ surface diffusion resistance at the interface between the zeolite porous matrix and water [3]. This suggests future experimental works to address these surface imperfections, as an essential prerequisite for improving water permeability of such membranes.

Finally, the complexity of water-solid interfaces will be fully revealed by “ugly’’ surfactants wrapping nanoparticle (NP) in aqueous solutions. Despite the large use of nanoparticle suspensions, tuning NP interactions and identifying desired NP assembly processes, in presence of surfactants, still represent a challenge for the design of nano-suspensions. We present a multiscale model for investigating nanoscale interfacial phenomena, stability, and aggregation of nanoparticles in aqueous solutions, including the dynamics of realistic surfactants [4]. In addition, the developed multiscale model is able to predict thermal properties of NP suspensions in reasonable agreement with the relevant experimental data from the literature, overcoming limitations of traditional theories obtained by coupling the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory with the kinetic theory of aggregation. Our results will enable the formulation of design rules for engineering NP aqueous suspensions suitable for a wide range of applications.

[1] E. Chiavazzo, M. Fasano, P. Asinari & P. Decuzzi, Nature Comm. 5, 3565, (2014).
[2] S.O. Diallo, PRE 92, 012312, (2015).
[3] M. Fasano, T. Humplik, A. Bevilacqua, M. Tsapatsis, E. Chiavazzo, E.N. Wang & P. Asinari, Nature Comm. 7, 12762, (2016).
[4] A. Cardellini, M. Alberghini, A.G. Rajan, R.P. Misra, D. Blankschtein & P. Asinari, submitted, (2018).